Protective device for machines such as bending presses, cutting machines, punching machines or the like

ABSTRACT

A guard means for machines, more particularly pressbrakes, guillotines, stamping machines and the like in the case of which a first machine part ( 10 ) performs working movements toward a second machine part ( 11 ). Between the machine parts a photoelectric detector arrangement { 19  and  20 ) is positioned and is attached to the moving machine part ( 10 ), a stop means being adapted to halt working motion of the moving machine part on interruption of a light beam. A control means for the working movement of the moving machine part ( 10 ) reduces the speed immediately prior to light beam interruption by the other machine part ( 11 ) to below a threshold limit speed.  
     By means of a speed measuring means ( 25  and  26 ) the working speed is measured and the stop means is deactivated below the predetermined threshold limit speed at least partially in order to be able to complete the working movement even in the case of interruption of the light beam by the other machine part ( 11 ). Such a speed measuring means may be also fitted externally to existing plant in a simple manner.

[0001] The invention relates to a guard means for machines, moreparticularly pressbrakes, guillotines, stamping machines and the like inthe case of which a first machine part performs working movements towarda second machine part, comprising a photoelectric detector arrangementpositioned between the machine parts and attached to the moving machinepart, a stop means adapted to halt working motion of the moving machineon interruption of a light beam and a deactivating means adapted todeactivate, at least directly prior to interruption of the light beam bythe other machinepart, the stop means.

[0002] Such guard means are disclosed in connection with pressbrakes forexample in the German patent publication 2,750,234, the European patentpublication 0 264 347 B the European patent publication 0 146 460 A orthe German patent publication 19,717,299 A. In the case of known guardmeans it is conventional for position monitoring valves to be employedto control the hydraulic drive of the moving machine part. Switchingover the rapid working movement to the slower working motion below thepredetermined threshold speed immediately before reaching the othermachine part is effected by resetting the valves' positions. Sensorsmonitor the valve position or other corresponding positions and theneffect, on reaching the corresponding position, deactivation of the stopmeans or, respectively, of the photoelectric detector arrangement.

[0003] It is more especially in the case of older machines thatupgrading modification of the machines themselves are necessary to mountthe necessary sensors and to adjust same, this being a slow expensiveprocess requiring some redesigning.

[0004] One object of the present invention is to so improve a guardmeans of the type initially mentioned that the deactivation of the stopmeans may be performed in a simpler fashion using devices, which may bereadily mounted on existing plant without need for adjustment.

[0005] In accordance with the invention this object is attained becausea speed measuring means for the moving machine part is provided and thedeactivating means comprises means for at least partly deactivating thestop means below a predetermined threshold speed, a control means forthe working movement of the moving machine part being adapted to reducethe speed immediately prior to interruption of the light beam by theother machine part to a speed below the threshold speed.

[0006] Owing to use of plain speed monitoring and speed control there isno need for later adjustment in position so that even for example in thecase of modifications of the photoelectric detector arrangement nomodification of the deactivating device will be necessary. A speedmeasuring means may be mounted in a simple manner externally on themachine or internally on the moving machine part. The possibilities forcontrol variations are substantially more extensive in the case of thespeed controlled guard means.

[0007] The dependent claims define features which represent advantageousdevelopments and improvements of the guard means defined in claim 1.

[0008] It is advantageous for the deactivating means to possess meansfor deactivating the stop means when machine parts are moving apart,that is to say on the detection of negative speed values, since herethere is no danger. In this respect the deactivating means may, inaccordance with an advantageous form of the invention, be designed withmeans for storage of that position, at which the threshold speed is notreached during working movement and for deactivating the stop meansuntil such position is reached again on the return motion of the movingmachine part. This means that the deactivating means or, respectively,the photoelectric detector cannot be activated, when in the course of areturn movement the moving machine part stops short of the storedposition, something which otherwise would lead to activating thephotoelectric detector arrangement and corresponding triggering of anundesired function.

[0009] In order to increase safety the speed measuring means comprisesat least two independently operating measurement modules arranged atdifferent positions, more particularly at two oppositely placed terminalportions of the moving machine part. This enhanced safety is moreparticularly produced by a comparison means for the data from themeasurement modules and by means of the deactivating means forpreventing deactivating of the stop means in the case of there being ano longer tolerable departure between data from the measurement module.Additionally it is possible in the case of discrepant data it isadvantageously possible to prevent an entire operating movement of themoving machine part, something which also serves to increase safety.

[0010] In accordance with an advantageous design means are provided forthe automatic detection of the overrun of the moving machine partfollowing a stop signal at least in the case of the first operatingmovement, the deactivating means possessing means for preventingdeactivation of the stop means on exceeding a predetermined maximumpredetermined and allowable overrun distance. This measurement as wellcontributes to increasing safety and in this case as well additionally acomplete working movement of the moving machine part may be prevented.

[0011] The means for automatically finding overrun preferably repeatsuch detection for each successive working movement until a permissibleoverrun distance has been detected. This means that operation of themachine with an excessive overrun distance is effectively prevented.

[0012] The speed measuring means preferably comprises at least onemeasurement module which possesses an incremental angular displacementsensor with a cable pulling means and/or an inductive sensor detectingthe movement of a magnetic strip, a differentiating means beingpreferably provided for conversion of displacement signals into speedsignals. Accordingly it is possible for position signals and speedsignals to be produced by the same measurement module.

[0013] One working example of the invention is represented in thedrawings and will be explained in the following description in detail.

[0014]FIG. 1 diagrammatically shows a pressbrake fitted with a speedcontrolled guard means in a longitudinal lateral elevation as a workingexample of the invention.

[0015]FIG. 2 is a diagrammatic block circuit diagram to explain themanner of operation.

[0016]FIG. 3 is a diagrammatic representation of a photoelectricdetector arrangement using three laser beams.

[0017] The pressbrake illustrated in FIG. 1 essentially comprises a toptool 10, which is able to be moved by means of hydraulic cylinders 7 and8 toward a stationary bottom tool 11. The opposite working movementdirection A is marked by a double arrow. In the case of an alternativedesign it would naturally be possible for the top tool to be stationaryand for the bottom tool to be the moving tool. The plate-like, elongatedtop tool 10 possesses a working portion 12 with a wedge-like crosssection, whereas the bottom tool 11 has a correspondingly wedge-likegroove 13, into which the working portion 12 plunges during workingmovement and accordingly bends or angles the sheet metal 14, supportedon the bottom tool 11.

[0018] The remaining parts of the inherently known pressbrake are notillustrated in order to make the drawing more straightforward. In theinitially mentioned prior art further details of such a pressbrake areto be found. The cross sectional configuration of the working portion 12and of the groove 13 may naturally be varied.

[0019] Respectively adjacent to mutually opposite narrow sides of thetop tool 10 guides 15 and 16 are attached, in which holding means 17 and18 for photoelectric detectors 19 and 20 are able to be moved as part ofa vertical setting movement, whose direction is represented by doublearrows B and which corresponds to the working direction A of motion.Each of the photoelectric detectors 19 and 20 comprises, in knownmanner, a laser transmitter and laser receiver, it being possible toreduce the number of transmitters by utilizing beam splitters or beamspreading means as is more particularly described in detail in the saidGerman patent publication 19,717,299 A.

[0020] The first photoelectric detector 19 and the second photoelectricdetector 20 are so arranged one above the other that same essentiallylie in the plane of motion of the line of bending, that is to say thetip of the working range 12 of the top tool 10. In this case thephotoelectric detector 19 primarily serves as a guard photoelectricdetector, whereas the photoelectric detector 20 primarily serves as anadjustment photoelectric detector and is arranged between thephotoelectric detector 19 and the top tool 10. Further photoelectricdetectors may be provided however arranged in parallelism to thedirection A of operating movement between such two photoelectricdetectors 19 and 20 or perpendicularly to such working direction A ofmovement, as is described in detail in the initially mentioned priorart. In lieu of laser photoelectric detectors it is naturally possibleto employ other known types of photoelectric detectors or other opticalguard means.

[0021] The guard function of the photoelectric detector arrangement isthat between the top tool 10 and the bottom tool 11 the closing actionis abruptly halted, if one of the laser beams 23 and 24 of thephotoelectric detectors 19 and 20 is interrupted, that is to say shouldsome object happen to be in the path of motion. Since such pressbrakesor similar machines are conventionally operated by hand, there is moreespecially a danger of the operator's hand or arm being in the path ofthe working movement, something which might possibly lead to it beingcrushed or even severed from the body. Since arrest of the closingmovement is also possible after a certain braking displacement, thedistance between the laser beam 23 and the laser beam 24 should be sodimensioned that anything finding its way into the path of movement isnot trapped or crushed. It will normally amount to 10 to 20 mm, forexample. As regards the description of adjustment of the photoelectricdetector arrangement attention is called to the initially mentionedprior art, since such adjustment is not as such part of the presentinvention.

[0022] The speed measuring means for the speed of the top tool 10comprises two measuring modules 25 and 26, which are arranged on adiagrammatically represented machine frame 27 in a stationary manner.This machine frame 27 furthermore bears the hydraulic cylinders 7 and 8for moving the top tool 10.

[0023] The left hand measuring module 25 is designed in the form of anincremental angle or rotation sensor in the case of which a cable 28attached to the guide 15, that is to say to the top tool, is wound andunwound on a pulley 29 or drum in the course of motion of the top tool10. The angular displacement of the pulley 29 is detected by aconventional angular incremental displacement or rotation sensor. Therotary movement of the pulley 29 is a measure of the speed of rotationof the top tool 10.

[0024] The right hand measuring module 26 possesses an inductive sensor30, past or through which, during motion of the top tool 10, a magneticmeasuring strip 21 attached to the guide 16 is moved. Instead of themeasuring means described it is possible to employ other means, such asfor example an inductive sensor with a perforated sheet metal tape or arack, a linear potentiometer or a transparent rule with a photoelectricdetector.

[0025] The working example illustrated in FIG. 1 provides for twodifferent modules 25 and 26 for sensing the speed of the top tool 10,two identical measuring modules however being utilized in practice. Thedifferent representation of the measuring modules 25 and 26 is onlyintended to make it clear that this different types of measuring modulescan be employed for finding the speed of the top tool 10. In addition tothe two designs of measuring modules it is naturally possible to employother designs of speed measuring module, which operate using other knownprinciples of speed measurement. To take the simplest case it would bepossible to employ only a single measurement module for speed.

[0026] The modus operandi of the guard means for the pressbrake depictedin figure will be explained in the following with reference to the blockcircuit diagram of FIG. 2. An electronic control device 31 controls thetwo hydraulic cylinders 7 and 8 and accordingly the movement of the toptool 10.

[0027] Initially, the control means 31 moves the top tool at a highspeed as far as a position just short of the bottom tool 11 or,respectively, the sheet metal 14 to be worked and then switches over toa slower working speed at which such sheet metal 14 is shaped. Theswitching over to the slower speed in this case takes place intermediatethe top tool 10 and the bottom tool 11 at a position in which the beam23 has not yet been interrupted by the sheet metal or the bottom tool 11so that a stop means 32, under the control of the photoelectricdetector, will not yet have abruptly arrested the working movement ofthe top tool at the point in time of switching over to the lower workingspeed owing to interruption of the light beam 23 or of another lightbeam. In order to prevent taking place during the slow working stroke aswell, in the case of which a limb of the operator could still bewithdrawn owing to the low closing speed (equal to 10 mm/s) even priorto being clamped and in the case of which the light beams of the lightbeam arrangement is interrupted by the sheet metal 14 and/or the bottomtool 11, the stop means 32 is deactivated by a deactivating means 33,which possesses a speed comparison means 34. In the latter the measuredspeed V1 of the top tool 10 is compared with a lower threshold speed Vo,which is gone below in the case of movement at the slow working speed.The stop means 32 is accordingly only switched on or, respectively,activated, when the speed V1 of the top tool 10 is greater than thelower threshold speed Vo. It is only in this case that the speedcomparison means 34 yields an output signal, by which by way of an ORgate 35 the stop means 32 is activated, something which in the oppositecase means that it is deactivated under this threshold speed or in thecase of a negative speed, that is to say during upward motion of the toptool 10.

[0028] The speed comparison means 34 accordingly causes automaticallydeactivating the stop means 32 on switching over to the low workingspeed and it causes it to remain deactivated in the course of the upwarddisplacement of the top tool 10, that is to say, during return movement.

[0029] In the case of many processing operations the top tool is resetagain within the safety distance, as from which switching over to thelower working speed takes place, in order then to perform a renewedworking movement toward the bottom tool. In this case it is necessary toensure that in the case of movements within this safety distance thestop means 32 remains deactivated, something which for example may beensured by storage of that position, at which switching over to thelower working speed took place. It is only on movement past such storedposition that the stop means 32 may be in principle activated again. Ifduring the upward motion of the top tool the stop means 32 is in anycase not activated, the it will be possible for this requirement to beautomatically fulfilled.

[0030] The arrangement of two modules 25 and 26 serves to increaseoperational reliability. A comparison means 36 is provided in thedeactivating means 33 for comparison of the measuring modules' 25 and 26speed signals V1 and V2. If these signals are not identical, the stopmeans 32 will remain constantly activated by the output signal of suchcomparison means 36 by way of the OR gate 35. Simultaneously, thecontrol means 31 for the hydraulic cylinders 7 and 8 is so driven bysuch output signal that a complete working stroke of the top tool 10 isprevented. This safety measure remains effective until the signals V1and V2 are again the same, that is to say until a reliable measurementof speed takes place.

[0031] Lastly the deactivating means 33 also comprises a monitoring unit37 for monitoring a maximum permissible overrun of the top tool 10following a stop command. This maximum overrun displacement will forexample amount to 10 mm. After turning on the electronic control means31, the latter will produce a check signal for the monitoring unit 37,for example simultaneously with the first working movement. This checksignal will mean that the instantaneous position of the top tool isstored and simultaneously the control means 31 will trigger stopping ofthe top tool 10. At the end of the stopping operation the position ofthe top tool 10 will be found and the difference, that is to say theoverrun Δs will be ascertained. This overrun Δs is compared with thestored maximum overrun So. In the case of there being an excessiveoverrun Δs the stop means 33 will be activated by way of the OR gate 35and held in the activate state. At the same time the correspondingoutput signal of the monitoring unit 37 acting via the control means 31will cause the performance of a complete working movement. In this casethe control means 31 will give rise to a further measuring operation forthe further overrun in the case of the same or at least one followingworking movement. It is only when a correct overrun is measured that itis possible for the output signal of the monitoring unit 37 to beswitched off or, respectively, deactivated again.

[0032] The measuring modules 25 and 26 described may serve both fordetecting position signals and also for the detection of speed signals,the speed signals being able to be obtained by differentiatingdisplacement signal.

[0033] In FIG. 3 a part of the top tool 10 is illustrated in an end-onview and, respectively, in section, an enhanced photoelectric detectorphotoelectric detector arrangement using three superposed laser beams 22through 24. The photoelectric detectors 19 and 20 may naturally beincluded in this photoelectric detector arrangement.

[0034] As compared with the already described laser beams 23 and 24 thelaser beam 22 is further removed from the top tool 10, that is to say itis nearer the bottom tool 11. The distance between the laser beams 22and 23 amounts to s. In a modified design of the block circuit diagramillustrated in FIG. 2, in cooperation with the arrangement depicted inFIG. 3 switching over to the lower working speed below the thresholdspeed Vo the stop means 32 is not completely deactivated and instead ismerely deactivated for the laser beam 22. An interruption of such laserbeam 22 can, after such partial deactivation, no longer lead tooperation of the stop means 32. It is only when the top tool 10,following switching over to the slow working speed, has moved along apredetermined stroke, equal to or less than the displacement s, thatthere will be a complete deactivation of the stop means 32 so that samecannot be triggered by any interruption of one of the lasers 22 through24.

[0035] The distance between the laser beam 23 and the laser beam 24 or,respectively, the top tool 10 amounts to 10 mm or less. The displacements amounts to 5 to 15 mm and accordingly serves to guard against therebeing long braking displacement. s is set in accordance with the brakingdistance so that the top tool will f. i. be moving at the slow speed inany case before the laser beam 23 is interrupted by the bottom tool 11.The distance between the laser beams 23 and 24 is made so small by thedesigner that there is no danger of any part of the operator's bodybeing introduced into the remaining narrow slot.

[0036] The guard means described is naturally not limited in itsapplication to pressbrakes and sheet metal guillotines and indeed may beemployed for all applications where machine parts move together andthere is a chance of part of an operator's body being crushed betweenthem. Furthermore the machine itself or parts thereof is also protectedagainst damage by the safety switching off means, should other objectsget in the way of the moving parts or tools of the machine and be likelyto damage same. The guard means of the invention may for example beapplied to stamping machines, automatically closing hinged or slidingdoors, planing machines or the like.

1. A guard means for machines, more particularly pressbrakes,guillotines, stamping machines and the like in the case of which a firstmachine part performs working movements toward a second machine part,comprising a photoelectric detector arrangement positioned between themachine parts and attached to the moving machine part, a stop meansadapted to halt working motion of the moving machine part oninterruption of a light beam and a deactivating means adapted todeactivate, at least directly prior to interruption of the light beam bythe other machine part, the stop means, characterized in that a speedmeasuring means (25 and 26) for the moving machine part (10) is providedand the deactivating means (33) comprises means (34) for at least partlydeactivating the stop means (32) below a predetermined threshold speed(Vo), a control means (31) for the working movement of the movingmachine part (10) being adapted to reduce the speed immediately prior tointerruption of the light beam by the other machine part (11) to a speedbelow the threshold speed (Vo).
 2. The guard means as claimed in claim1, characterized in that the deactivating means (33) comprises means(34) for deactivating the stop means (32) on movement of the machineparts apart.
 3. The guard means as claimed in claim 2, characterized inthat the deactivating means (33) possesses means for the storage of thatposition, at which during the working motion the threshold limit speedis gone below, and for deactivating the stop means (32) until suchposition is re-attained on return motion of the moving machine part(10).
 4. The guard means as claimed in any one of the preceding claims,characterized in that the speed measuring means (25 and 26) includes atleast two independently operating measuring modules arranged atdifferent points, more particularly on two opposite end portions of themoving machine part (10).
 5. The guard means as claimed in claim 4,characterized in that a comparison means (36) is provided for the datafrom the measuring modules of the speed measuring means (25 and 26) andin that the deactivating means (33) comprises means for preventingdeactivation of the stop means (32) in the case of data (V1 and V2)departing from one another by more than a tolerance value.
 6. The guardmeans as claimed in claim 5, characterized in that means are providedfor preventing a complete working movement of the moving machine part(10) in the case of data (V1 and V2) departing form one another by morethan a preset tolerance value.
 7. The guard means as claimed in any oneof the preceding claims, characterized in that means (37) are providedfor automatically finding the overrun (Δs) of the moving machine part(10) following a stop signal at least in the case of the first workingmovement and in that the deactivating means (33) possesses means fordeactivating the stop means (32) in the case of a predetermined maximumpermissible overrun (So) being exceeded.
 8. The guard means as claimedin claim 7, characterized in that means are provided to prevent acomplete working movement of the moving machine part (10) in the case ofa predetermined maximum permissible overrun (So) being exceeded.
 9. Theguard means as claimed in claim 7 or in claim 8, characterized in thatthe means (37) for automatically sensing the overrun of the movingmachine part (10) perform such sensing action repeatedly until apredetermined maximum permissible overrun (So) is detected.
 10. Theguard means as claimed in any one of the preceding claims, characterizedin that the speed measuring means (25 and 26) possesses at least onemeasuring module, which has an incremental angular displacement sensor(29) having a cable (28) and/or an inductive sensor (30) responsive tothe movement of a magnetic strip (21) of a perforated sheet metalelement or a rack and/or a transparent rule with a photoelectricdetector and/or a linear potentiometer, preferably at least onedifferentiating means being provided for conversion of the displacementsignals into speed signals.
 11. The guard means as claimed in any one ofthe preceding claim, characterized in that means are provided toforestall triggering of the stop means (32) on interruption of thephotoelectric detector arrangement's light beam (22) furthest from themoving machine part below the predetermined threshold limit speed, acomplete deactivation of the stop means (32) only being produced afterthe moving machine part's (10) movement along a predetermined path (s)after switching over of its working speed to below the threshold limitspeed (Vo).
 12. The guard means as claimed in claim 11, characterized inthat the predetermined displacement (s) is equal to or smaller than thedistance between the light beam (22) furthest from the moving machinepart (10 and the next nearest one (23).